Process for producing polyoxyethylene sorbitan fatty acid ester

ABSTRACT

A process for producing a polyoxyethylene sorbitan fatty acid ester in which the bitterness just after the production and the bitterness with the lapse of time is suppressed. The process of the invention includes reacting an ester (component A) of a fatty acid having 10 to 22 carbon atoms and a monohydric alcohol having 1 to 3 carbon atoms with at least either (component B) of sorbitol and sorbitan to form a sorbitan fatty acid ester and adding ethylene oxide to the sorbitan fatty acid ester, thereby producing a polyoxyethylene sorbitan fatty acid ester, which is characterized that the following steps (a) to (d) are contained: (a) the component B is provided in the form of a 50 to 90% by weight aqueous solution and mixed with the component A and dehydration was performed until a water content in the system reaches 1.0% by weight or less based on the total weight of the components A and B; (b) 1 to 10% by weight of a monohydric alcohol having 1 to 3 carbon atoms and 0.1 to 1.0% by weight of an alkali catalyst based on the total weight of the components A and B are added at 50 to 90° C.; (c) a transesterification reaction is performed under a nitrogen stream at a reaction temperature of 140 to 190° C. to thereby obtain a sorbitan fatty acid ester; (d) ethylene oxide is added thereto at a reaction temperature of 70 to 130° C.

TECHNICAL FIELD

The present invention relates to a process for producing apolyoxyethylene sorbitan fatty acid ester in which an increase in thebitterness with the lapse of time is suppressed.

BACKGROUND ART

A polyoxyethylene sorbitan fatty acid ester obtained by adding ethyleneoxide to a sorbitan fatty acid ester which is a partial ester ofsorbitol or sorbitan and a fatty acid is known to be excellent inproperties such as emulsifying ability, dispersing ability, and wettingability and has been employed in a wide variety of uses such ascosmetics, lubricants, synthetic resins, and detergents.

Moreover, among the polyoxyethylene sorbitan fatty acid esters,polysorbate 80 is a substance described in Japanese Pharmacopoeia andpolysorbates 20, 40, 60, and 65 are substances described in JapanesePharmaceutical Excipients and they are generally widely used aspharmaceutical additives. Furthermore, in Europe and America, thesepolysorbates have actual performance of being permitted and haveemployed as food additives and, also in Japan, are in the course ofpreparation for permission at an early date as food additives. Thus, thepolyoxyethylene sorbitan fatty acid esters have used in a wide range offields.

However, as physical properties of the polyoxyethylene sorbitan fattyacid esters, they are substances which generally give feeling of bittertaste, oxidation odor, and deterioration odor, for example, as describedthat “the taste is slightly bitter and slight characteristic odor ispresent” as properties of polysorbates 40, 60, and 65 in JapanesePharmaceutical Excipients and polysorbate 80 in Japanese Pharmacopoeia.Therefore, they are avoided in some cases in the fields such as foodsand oral cosmetics where their taste is greatly regarded as important.

As production processes for improving the bitterness of thepolyoxyethylene sorbitan fatty acid esters, there have been reported aprocess of performing a steam treatment or a distillation treatment(Patent Document 1) and a process of performing a dehydration-adsorptiontreatment with a specific adsorbent in the presence of water (PatentDocument 2).

-   Patent Document 1: JP-A-2005-23227-   Patent Document 2: JP-A-2007-91852

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

In the processes described in Patent Documents 1 and 2, although thebitterness just after the production has been improved to some degreebut the degree has not been sufficiently satisfactory. Furthermore, ithas been found that these processes have a problem that bitternessincreases with the lapse of time. In the uses such as foods and oralcosmetics, there has been desired a polyoxyethylene sorbitan fatty acidester in which bitterness does not increase with the lapse of time.

An object of the invention is to provide a process for producing apolyoxyethylene sorbitan fatty acid ester in which the bitterness justafter the production is suppressed and also an increase in thebitterness with the lapse of time is suppressed.

Means for Solving the Problems

The present invention relates to a process for producing apolyoxyethylene sorbitan fatty acid ester of the invention comprisingreacting an ester (component A) of a fatty acid having 10 to 22 carbonatoms and a monohydric alcohol having 1 to 3 carbon atoms with at leasteither (component B) of sorbitol and sorbitan to obtain a sorbitan fattyacid ester and adding ethylene oxide to the sorbitan fatty acid ester,thereby producing a polyoxyethylene sorbitan fatty acid ester, whichcomprises:

(a) a step of providing the component B in the form of a 50 to 90% byweight aqueous solution, mixing it with the component A, and performingdehydration until a water content in the system reaches 1.0% by weightor less based on the total weight of the components A and B;

(b) a step of adding 1 to 10% by weight of a monohydric alcohol having 1to 3 carbon atoms and 0.1 to 1.0% by weight of an alkali catalyst basedon the total weight of the components A and B at 50 to 90° C.;

(c) a step of performing a transesterification reaction under a nitrogenstream at a reaction temperature of 140 to 190° C. to thereby obtain asorbitan fatty acid ester; and

(d) a step of adding ethylene oxide to the sorbitan fatty acid ester ata reaction temperature of 70 to 130° C.

Advantage of the Invention

The polyoxyethylene sorbitan fatty acid ester obtained by the inventionshows not only an improvement in the bitterness just after theproduction and also suppression of an increase in the bitterness withthe lapse of time, so that it can be most suitably used in foods,cosmetics, medicated cosmetics, and medicines.

BEST MODE FOR CARRYING OUT THE INVENTION

The following will describe the invention in detail.

In the invention, a polyoxyethylene sorbitan fatty acid ester isobtained by reacting at least one kind of fatty acid ester (component A)of a fatty acid having 10 to 22 carbon atoms and a monohydric alcoholhaving 1 to 3 carbon atoms with sorbitol and/or sorbitan (component B)to obtain a sorbitan fatty acid ester and adding ethylene oxide thereto.

(Regarding Fatty Acid Ester)

The fatty acid ester as (component A) of the invention is an ester of asaturated or unsaturated fatty acid having 10 to 22 carbon atoms and amonohydric alcohol having 1 to 3 carbon atoms. In this case, the fattyacid may be a natural fatty acid or a synthetic fatty acid, may besaturated one or unsaturated one, and further may be linear one orbranched one. Specific examples of such a fatty acid include capricacid, lauric acid, myristic acid, palmitic acid, margaric acid, stearicacid, arachidic acid, behenic acid, palmitoleic acid, oleic acid, erucicacid, isostearic acid, and the like. Preferred is a saturated orunsaturated linear fatty acid having 10 to 18 carbon atoms.

On the other hand, as the monohydric alcohol having 1 to 3 carbon atomsfor esterifying the above-described fatty acid, there may be, forexample, mentioned methanol, ethanol, isopropanol, n-propanol, and thelike, and may be preferably methanol and ethanol, more preferablymethanol.

(Regarding Sorbitol and/or Sorbitan)

As sorbitol and/or sorbitan as (component B) of the invention,commercially available one can be used. Moreover, from the viewpoint ofinfluence on color-tone deterioration, odor, bitterness, and the like,the aldehyde content of (component B) is preferably 50 ppm or less.

The aldehyde content of (component B) can be reduced by treatment withan appropriate adsorbent. As the adsorbent, one containing a compositemetal oxide activated by baking can be suitably used and the purpose canbe achieved by a silica/alumina-based adsorbent, zeolite, hydrotalcite,magnesium oxide/aluminum oxide composite metal oxide, or the like.

(Measurement Method of Aldehyde Content)

The aldehyde content of sorbitol and/or sorbitan can be measured by themethod shown below.

(1) One gram of a sample is placed in a test tube with ground-in stopperand a fuchsine sulfite solution (Note 1) is added, followed by tightsealing. They are mixed and allowed to stand at room temperature for 30minutes.

(2) Absorbance of the solution at a wavelength of 562 nm and a cellwidth of 10 mm is measured by means of an ultraviolet-visiblespectrophotometer (FT/IR-410 manufactured by JASCO Corporation).

(3) A blank test is performed in the same manner using 1 g of waterinstead of the sample solution and absorbance on this occasion is 0(standard).

(4) The same operations are performed using a formaldehyde standardsolution (Note 2) to prepare a calibration curve and the content of thealdehyde contained in the sample is determined from the calibrationcurve.

(Note 1: Preparation of Fuchsine Sulfite Solution)

Basic fuchsine (200 mg) is weighed into 200 mL of a messflask and 120 mLof warm water is added to dissolve the fuchsine, followed by standing tocool. A solution obtained by dissolving 2 g of anhydrous sodium sulfitein 20 mL of water and 2 mL of hydrochloric acid are added thereto andthe whole is diluted to a marked line with water. The solution isallowed to stand for at least 1 hour before use, and disappearance ofpink color is confirmed.

(Note 2: Preparation of Formaldehyde Standard Solutions)

Solutions having a formaldehyde concentration of 1 ppm, 10 ppm, 50 ppm,and 100 ppm are prepared and they are used as standard solutions forcalibration curve preparation.

(Transesterification Reaction of Sorbitol and/or Sorbitan with FattyAcid Ester)

As a production step of the sorbitan fatty acid ester of the invention,there is a step (step a) of providing (component B) as a 50 to 90% byweight aqueous solution and performing dehydration until the watercontent in the reaction system reaches 1.0% by weight or less based onthe total weight of (component A) and (component B).

Sorbitol is a solid and sorbitan is a highly viscous liquid at ordinarytemperature. Therefore, when the compound is mixed with a fatty acidester as it is, it aggregates in the fatty acid ester. Thus, it isnecessary that (component B) be mixed as an aqueous solution with thefatty acid ester and water in the reaction system be gradually removedby dehydration.

The conditions for dehydration thereafter are not particularly limitedbut the dehydration can be performed under a nitrogen atmosphere at 90to 110° C. under 20 kPa or less for a short period of time. In the casewhere the water content after the dehydration exceeds 1.0% by weight,the fatty acid ester is partially hydrolyzed to generate a fatty acid,so that the reactivity decreases. In this case, a caramel-like substanceis excessively formed by heat hysteresis owing to an increase in thereaction time, consequently causing bitterness.

Next, there is a step (step b) of adding 1 to 10% by weight of amonohydric alcohol having 1 to 3 carbon atoms and 0.1 to 1.0% by weightof an alkali catalyst at 50 to 90° C. based on the total weight of(component A) and (component B). In the transesterification reactionbetween (component A) and (component B), the reaction in a heterogeneousstate at an early stage is a rate-determining step and the reaction rateat the early reaction step can be enhanced by adding the monohydricalcohol having 1 to 3 carbon atoms.

As the monohydric alcohol having 1 to 3 carbon atoms, there may be, forexample, mentioned methanol, ethanol, isopropanol, n-propanol, and thelike, and may be preferably methanol and ethanol, more preferablymethanol. In the case of a monohydric alcohol having 4 or more carbonatoms or a polyhydric alcohol, it has a high boiling point and thusthere is a risk that it may remain in a product, so that the case is notpreferred.

The amount of the monohydric alcohol having 1 to 3 carbon atoms to beadded is 1 to 10% by weight, preferably 2 to 8% by weight, and morepreferably 3 to 6% by weight based on the total amount of (component A)and (component B). When the amount is less than 1% by weight, thereaction promoting effect in a heterogeneous state at an early stage isinsufficient. When the amount exceeds 10% by weight, not only thereaction promoting effect is not obtained but also a large amount of themonohydric alcohol should be recovered and a risk that the monohydricalcohol may remain in the product increases, so that the case is notpreferred.

Moreover, the temperature for adding the monohydric alcohol having 1 to3 carbon atoms is 50 to 90° C. and preferably, it is preferred to add itat a temperature lower than the boiling point of the monohydric alcoholto be added. In the case where the temperature for the addition is lowerthan 50° C., the viscosity of (component B) increases and the stirringefficiency lowers. In the case where the temperature exceeds the boilingpoint of the monohydric alcohol, there is a risk of bumping of themonohydric alcohol, so that the case is not preferred in view of workingsafety.

The amount of the alkali catalyst to be added in (step b) is 0.1 to 1.0%by weight, preferably 0.2 to 0.9% by weight, and more preferably 0.3 to0.8% by weight based on the total amount of (component A) and (componentB). In the case where the amount of the alkali catalyst is less than0.1% by weight, the reaction rate is remarkably lowered. In the casewhere the amount exceeds 1.0% by weight, the caramel-like substance isexceedingly formed, consequently causing bitterness. Specific examplesof the alkali catalyst include sodium hydroxide, potassium hydroxide,sodium methoxide, sodium carbonate, and the like. Preferred is sodiummethoxide. Moreover, the alkali catalyst may be dissolved in themonohydric alcohol having 1 to 3 carbon atoms beforehand and then addedor may be added separately. However, when the solubility of the alkalicatalyst in the reaction system is considered, it is rather preferredthat both substances be dissolved beforehand and then added.

After the addition of the alkali catalyst and the monohydric alcoholhaving 1 to 3 carbon atoms, there is a step (step c) of performingtransesterification reaction at a reaction temperature of 140 to 190° C.under a nitrogen stream. The reaction temperature is preferably 150 to185° C. and more preferably 160 to 180° C. In the case where thereaction temperature is lower than 140° C., the reaction rate isremarkably lowered and the caramel-like substance is exceedingly formedby heat hysteresis owing to an increase in the reaction time,consequently causing bitterness. Also in the case where the temperatureexceeds 190° C., the caramel-like substance is formed by condensation ofsorbitan and sorbitol, consequently causing bitterness.

With regard to the reaction pressure in (step c), the reaction may beperformed at normal pressure but the reaction rate can be enhanced byperforming the reaction at 1 to 20 kPa. The pressure at the reaction ispreferably 2 to 15 kPa and more preferably 3 to 10 kPa. When thereaction pressure exceeds 20 kPa, the effect of enhancing the reactionrate decreases.

(Regarding Sorbitan Fatty Acid Ester)

The ratio of (component A) to (component B) used in the invention variesdepending on the average degree of substitution (degree ofesterification) of the objective sorbitan fatty acid ester but it ispreferred to use (component A) in an amount of 0.5 to 3.5 molarequivalents, preferably 1.0 to 2.0 molar equivalents. Depending on thedifference in the degree of esterification, the ester is classified intoa sorbitan monofatty acid ester, a sorbitan sesquifatty acid ester, asorbitan difatty acid ester, a sorbitan trifatty acid ester, or thelike.

(Regarding EO Addition Reaction and Purification)

The polyoxyethylene sorbitan fatty acid ester of the invention isobtained by adding ethylene oxide to a sorbitan fatty acid ester.

The average number of moles of added ethylene oxide is preferably 1 to50, particularly in the case of use as food additives, furtherpreferably 15 to 25, and most preferably 20. In the addition reaction ofethylene oxide to the sorbitan fatty acid ester, catalysts hithertoknown can be used without particular limitation and, for example, analkali metal catalyst such as potassium hydroxide, sodium hydroxide, orsodium methoxide, fatty acid soaps, and the like are employed. Thereaction temperature for the addition reaction of ethylene oxide is 70to 130° C., more preferably 80 to 120° C., and further preferably 90 to110° C. When the reaction temperature is lower than 70° C., the reactionhardly proceeds and when the temperature is higher than 130° C., such atemperature causes bitterness of the product. Moreover, the reactionpressure is preferably 0.1 to 0.8 MPa, and further preferably 0.1 to 0.4MPa.

In the invention, in order to neutralize the alkali catalyst containedin the polyoxyethylene sorbitan fatty acid ester obtained after theaddition reaction of ethylene oxide, a mineral acid such as phosphoricacid or sulfuric acid, a short-chain aliphatic monocarboxylic acid suchas formic acid, acetic acid, caproic acid, or lactic acid, a polybasiccarboxylic acid such as oxalic acid, succinic acid, malic acid, adipicacid, or citric acid, an aromatic monocarboxylic acid such as benzoicacid or salicylic acid, an aromatic polybasic acid such as phthalicacid, terephthalic acid, or isophthalic acid, or the like may be added,salting-out and washing with water may be performed, or a treatment withan ion-exchange resin may be performed. These treatments may beperformed with repeating each operation or with doubly performingdifferent treatments. Furthermore, if necessary, purification with adiscoloration treatment, removal of water and solvents, steamdeodorization, ion exchange resin, or active carbon may be performed orwhen an unnecessary substance is present, it may be removed bycentrifugation or filtration.

The polyoxyethylene sorbitan fatty acid ester obtained through theaddition reaction of ethylene oxide and subsequent neutralization andpurification is classified depending on the kind of the fatty acid andthe difference in the degree of esterification. For example, oneobtained by addition of 20 moles of ethylene oxide to sorbitanmonolaurate is called “polyoxyethylene (20) sorbitan monolaurate(polysorbate 20)”, one obtained by addition of 20 moles of ethyleneoxide to sorbitan monostearate is called “polyoxyethylene (20) sorbitanmonostearate (polysorbate 60)”, one obtained by addition of 20 moles ofethylene oxide to sorbitan tristearate is called “polyoxyethylene (20)sorbitan tristearate (polysorbate 65)”, and one obtained by addition of20 moles of ethylene oxide to sorbitan monooleate is called“polyoxyethylene (20) sorbitan monooleate (polysorbate 80)”.

In the invention, in order to prevent the deterioration with the lapseof time after neutralization and purification of the polyoxyethylenesorbitan fatty acid ester, one kind or two or more kinds of antioxidantssuch as sorbic acid, dibutylhydroxytoluene, dibutylhydroxyanisole,propyl gallate, isopropyl citrate, guaiacic acid, disodiumethylenediaminetetraacetate, and dl-α-tocopherol can be added.

Since the bitterness just after production and an increase in thebitterness with the lapse of time in the polyoxyethylene sorbitan fattyacid ester of the invention are small as compared with those inconventional one, the polyoxyethylene sorbitan fatty acid ester can besuitably used in medicines, medicated cosmetics, cosmetics, food uses,and the like, particularly in food uses.

EXAMPLES

The following will describe the invention further in detail withreference to Examples and Comparative Examples. With regard torespective synthetic products, sensory evaluation on the bitterness justafter synthesis and the bitterness after 6 months from the synthesis(under storage at 25° C.) was performed. Synthetic conditions andevaluation results are shown in Table 1.

Example 1 Synthesis of Polyoxyethylene (20) Sorbitan Monooleate

After 469 g of a 70% by weight sorbitan aqueous solution (aldehyde valueof sorbitan: 5.0 ppm) and 947 g of methyl oleate were charged into a2000 mL four-neck flask fitted with a stirring apparatus, a thermometer,and a nitrogen gas inlet, dehydration was performed at 110° C. under anitrogen stream at normal pressure for 1 hour and further at 110° C.under a nitrogen stream at 4 kPa for 1 hour. The whole was cooled to 65°C. and, after 51.0 g of a 10% by weight sodium methoxide methanolsolution and 0.64 g of sodium hypophosphite were added thereto, thetemperature was raised under a nitrogen stream at normal pressure to170° C. as a reaction temperature. After the temperature reached 170°C., the pressure was reduced to 6.5 kPa and the reaction was carried outunder a nitrogen stream. At the time point when the spot of methyloleate as a raw material disappeared on thin-layer chromatography, itwas judged that the reaction was completed. The time required for thereaction was 8 hours and, after the completion of the reaction wasconfirmed, the mixture was filtrated at 80° C. to obtain sorbitanmonooleate.

(Measurement Conditions for Thin-Layer Chromatography)

TLC plate: silica gel 60 manufactured by Merck & Co., Inc.

Developing solvent: chloroform/n-butanol=97/3 (v/v)

Diluent solvent: chloroform

Dilution concentration: a sample (sorbitan fatty acid ester) solution=1w/v %

a standard (fatty acid methyl ester) solution=0.1 w/v %

Spotting amount: 1 μL

Color-developing solution: a phosphoric acid/copper sulfate aqueoussolution (156 g of copper sulfate pentahydrate and 135 g of an 85% byweight of phosphoric acid aqueous solution is weighed into a 1 Lmessflask and diluted to the marked line)

Color-developing method: the phosphoric acid/copper sulfate aqueoussolution is applied and, after drying, is heated in aconstant-temperature chamber at 170° C. for 15 minutes.

Into an autoclave was charged 668 g of sorbitan monooleate obtained bythe transesterification reaction. After the atmosphere in the autoclavewas replaced with dry nitrogen, the compound was heated to 100° C. withstirring. Subsequently, 1332 g of ethylene oxide was added dropwise at100° C. by means of a dropping apparatus to cause a reaction and thewhole was stirred for 2 hours as it was to complete the reaction. Thereaction composition was taken out of the autoclave and was neutralizedwith an 85% by weight phosphoric acid aqueous solution to adjust the pHto 6 to 7. Thereafter, in order to remove water contained therein,dehydration was performed at 100° C. under a nitrogen stream at 6.5 kPafor 1 hour. The product was filtrated at 80° C. to obtainpolyoxyethylene (20) sorbitan monooleate.

Example 2 Synthesis of Polyoxyethylene (20) Sorbitan Monostearate

After 469 g of a 70% by weight sorbitan aqueous solution (aldehyde valueof sorbitan: 7.4 ppm) and 872 g of methyl stearate were charged into a2000 mL four-neck flask fitted with a stirring apparatus, a thermometer,and a nitrogen gas inlet, dehydration was performed at 110° C. under anitrogen stream at normal pressure for 1 hour and further at 110° C.under a nitrogen stream at 4 kPa for 1 hour. The whole was cooled to 65°C. and, after 30.0 g of a 20% by weight sodium methoxide methanolsolution and 0.06 g of sodium hypophosphite were added thereto, washeated under a nitrogen stream at normal pressure to 190° C. as areaction temperature. After the temperature reached 190° C., pressurewas reduced to 6.5 kPa and the reaction was carried out under a nitrogenstream. At the time point when the spot of methyl stearate as a rawmaterial disappeared on thin-layer chromatography, it was judged thatthe reaction was completed. The reaction time was 5 hours and, after thecompletion of the reaction was confirmed, the mixture was filtrated at80° C. to obtain sorbitan monostearate.

Into an autoclave was charged 642 g of sorbitan monostearate obtained bythe transesterification reaction. After the atmosphere in the autoclavewas replaced with dry nitrogen, the compound was heated to 100° C. withstirring. Subsequently, 1358 g of ethylene oxide was added dropwise at100° C. by means of a dropping apparatus to cause a reaction and thewhole was stirred for 2 hours as it was to complete the reaction. Thereaction composition was taken out of the autoclave and was neutralizedwith an 85% by weight phosphoric acid aqueous solution to adjust the pHto 6 to 7. Thereafter, in order to remove water contained therein,dehydration was performed at 100° C. under a nitrogen stream at 6.5 kPafor 1 hour. The product was filtrated at 80° C. to obtainpolyoxyethylene (20) sorbitan monostearate.

Example 3 Synthesis of Polyoxyethylene (20) Sorbitan Monolaurate

After 469 g of a 70% by weight sorbitan aqueous solution (aldehyde valueof sorbitan: 6.5 ppm) and 556 g of methyl laurate were charged into a2000 mL four-neck flask fitted with a stirring apparatus, a thermometer,and a nitrogen gas inlet, dehydration was performed at 110° C. under anitrogen stream at normal pressure for 1 hour and further at 110° C.under a nitrogen stream at 4 kPa for 1 hour. The whole was cooled to 65°C. and, after 35.4 g of a 5% by weight sodium methoxide methanolsolution and 0.44 g of sodium hypophosphite were added thereto, washeated under a nitrogen stream at normal pressure to 150° C. as areaction temperature. After the temperature reached 150° C., thereaction was carried out under a nitrogen stream at normal pressure. Atthe time point when the spot of methyl laurate as a raw materialdisappeared on thin-layer chromatography, it was judged that thereaction was completed. The reaction time was 8 hours and, after thecompletion of the reaction was confirmed, the product was filtrated at80° C. to obtain sorbitan monolaurate.

Into an autoclave was charged 574 g of sorbitan monolaurate obtained bythe transesterification reaction. After the atmosphere in the autoclavewas replaced with dry nitrogen, the compound was heated to 100° C. withstirring. Subsequently, 1426 g of ethylene oxide was added dropwise at100° C. by means of a dropping apparatus to cause a reaction and thewhole was stirred for 2 hours as it was to complete the reaction. Thereaction composition was taken out of the autoclave and was neutralizedwith an 85% by weight phosphoric acid aqueous solution to adjust the pHto 6 to 7. Thereafter, in order to remove water contained therein,dehydration was performed at 100° C. under a nitrogen stream at 6.5 kPafor 1 hour. The product was filtrated at 80° C. to obtainpolyoxyethylene (20) sorbitan monolaurate.

Example 4 Synthesis of Polyoxyethylene (20) Sorbitan Monooleate

After 469 g of a 70% by weight sorbitan aqueous solution (aldehyde valueof sorbitan: 5.0 ppm) and 947 g of methyl oleate were charged into a2000 mL four-neck flask fitted with a stirring apparatus, a thermometer,and a nitrogen gas inlet, dehydration was performed at 110° C. under anitrogen stream at normal pressure for 1 hour and further at 110° C.under a nitrogen stream at 4 kPa for 1 hour. The whole was cooled to 65°C. and, after 51.0 g of a 10% by weight sodium methoxide methanolsolution and 0.64 g of sodium hypophosphite were added thereto, washeated under a nitrogen stream at normal pressure to 180° C. as areaction temperature. After the temperature reached 180° C., thereaction was carried out under a nitrogen stream at normal pressure. Atthe time point when the spot of methyl oleate as a raw materialdisappeared on thin-layer chromatography, it was judged that thereaction was completed. The reaction time was 12 hours and, after thecompletion of the reaction was confirmed, the product was filtrated at80° C. to obtain sorbitan monooleate.

Into an autoclave was charged 668 g of sorbitan monooleate obtained bythe transesterification reaction. After the atmosphere in the autoclavewas replaced with dry nitrogen, the compound was heated to 120° C. withstirring. Subsequently, 1332 g of ethylene oxide was added dropwise at120° C. by means of a dropping apparatus to cause a reaction and thewhole was stirred for 2 hours as it was to complete the reaction. Thereaction composition was taken out of the autoclave and was neutralizedwith an 85% by weight phosphoric acid aqueous solution to adjust the pHto 6 to 7. Thereafter, in order to remove water contained therein,dehydration was performed at 100° C. under a nitrogen stream at 6.5 kPafor 1 hour. The product was filtrated at 80° C. to obtainpolyoxyethylene (20) sorbitan monooleate.

Comparative Example 1 Synthesis of Polyoxyethylene (20) SorbitanMonooleate

After 497 g of a 70% by weight sorbitol aqueous solution (aldehyde valueof sorbitol: 5.0 ppm), 863 g of oleic acid, 3.0 g of sodium carbonate,and 1.7 g of sodium hypophosphite were charged into a 2000 mL four-neckflask fitted with a stirring apparatus, a thermometer, and a nitrogengas inlet, replacement with nitrogen was performed at room temperaturefor 30 minutes. Thereafter, the temperature was raised stepwise to 110°C., 140° C., and 170° C. After the temperature reached 170° C. as areaction temperature, the pressure was reduced to 6.5 kPa and thereaction was carried out under a nitrogen stream. At the time point whenthe spot of oleic acid as a raw material disappeared on thin-layerchromatography, it was judged that the reaction was completed. Thereaction time was 20 hours and, after the completion of the reaction wasconfirmed, the product was filtrated at 80° C. to obtain sorbitanmonooleate.

Into an autoclave were charged 668 g of sorbitan monooleate and 1.0 g ofsodium hydroxide as a catalyst. After the atmosphere in the autoclavewas replaced with dry nitrogen, the catalyst was completely dissolved at100° C. with stirring. Subsequently, 1332 g of ethylene oxide was addeddropwise at 100° C. by means of a dropping apparatus to cause a reactionand the whole was stirred for 2 hours as it was to complete thereaction. The reaction composition was taken out of the autoclave andwas neutralized with an 85% by weight phosphoric acid aqueous solutionto adjust the pH to 6 to 7. Thereafter, in order to remove watercontained therein, dehydration was performed at 100° C. under a nitrogenstream at 6.5 kPa for 1 hour. The product was filtrated to obtainpolyoxyethylene (20) sorbitan monooleate.

Comparative Examples 2 to 8 Synthesis of Polyoxyethylene (20) SorbitanMonooleate

The polyoxyethylene (20) sorbitan monooleate shown in ComparativeExamples 2 to 8 was formed under the conditions shown in Table 1 basedon the synthetic example of Example 1.

Comparative Example 9 Synthesis of Polyoxyethylene (20) SorbitanMonooleate

After 497 g of a 70% by weight sorbitol aqueous solution (aldehyde valueof sorbitol: 5.0 ppm), 863 g of oleic acid, 3.0 g of sodium carbonate,and 1.7 g of sodium hypophosphite were charged into a 2000 mL four-neckflask fitted with a stirring apparatus, a thermometer, and a nitrogengas inlet, replacement with nitrogen was performed at room temperaturefor 30 minutes. Thereafter, the temperature was raised stepwise to 110°C., 140° C., 190° C., and 230° C. After the temperature reached 230° C.as a reaction temperature, the reaction was carried out under a nitrogenstream at normal pressure. At the time point when the spot of oleic acidas a raw material disappeared on thin-layer chromatography, it wasjudged that the reaction was completed. The reaction time was 5 hoursand, after the completion of the reaction was confirmed, the product wasfiltrated at 80° C. to obtain sorbitan monooleate.

To 1000 g of monooleic acid obtained by the esterification, 50 g ofwater and 20 g of Kyoward 2000 (manufactured by Kyowa Chemical IndustryCo., Ltd., magnesium oxide: 60% by weight, aluminum oxide: 30% byweight, content of composite metal oxide: 90% by weight, and loss ondrying: 0.8% by weight) were added, and the whole was treated at 80° C.for 1 hour under a nitrogen stream with stirring. Then, the product wastreated at 6.5 kPa at 100° C. for 1 hour to remove water and theadsorbent was removed by filtration.

Into an autoclave were charged 668 g of sorbitan monooleate treated withthe adsorbent and 1.0 g of sodium hydroxide as a catalyst. After theatmosphere in the autoclave was replaced with dry nitrogen, the catalystwas completely dissolved at 100° C. with stirring. Subsequently, 1332 gof ethylene oxide was added dropwise at 100° C. by means of a droppingapparatus to cause a reaction and the whole was stirred for 2 hours asit was to complete the reaction. The reaction composition was taken outof the autoclave and was neutralized with an 85% by weight phosphoricacid aqueous solution to adjust the pH to 6 to 7. Thereafter, in orderto remove water contained therein, dehydration was performed at 100° C.under a nitrogen stream at 6.5 kPa for 1 hour. The product was filtratedto obtain polyoxyethylene (20) sorbitan monooleate.

To 500 g of polyoxyethylene (20) sorbitan monooleate synthesized, 25 gof water and 10 g of Kyoward 2000 were added, and dehydration wasperformed at 80° C. under a nitrogen stream at normal pressure for 1hour and at 110° C. under a nitrogen stream at 6.5 kPa for 1 hour. Theproduct was filtrated at 80° C. to remove the adsorbent, therebyobtaining a synthetic product.

Comparative Example 10 Synthesis of Polyoxyethylene (20) SorbitanMonooleate

Into 500 g of polyoxyethylene (20) sorbitan monooleate before adsorbenttreatment synthesized in Comparative Example 9 was introduced 50 g ofsteam under conditions of 120° C. and 6.5 kPa, thereby performing steamtreatment. Thereafter, dehydration was performed at 110° C. at 4 kPaunder a nitrogen stream for 1 hour and the product was filtrated at 80°C. to obtain a synthetic product.

[Sensory Evaluation Regarding Bitterness]

With regard to the above Examples and Comparative Examples, sensoryevaluation of each synthetic product regarding bitterness was performedby 10 panelists, within 3 days after synthesis and after 6 months fromsynthesis (storage at 25° C.). For comparative measurement ofbitterness, evaluation was performed by placing the polyoxyethylenesorbitan fatty acid ester directly on the tongue, evaluating bitternessfelt as the following 5 stages when it was tasted for about 10 seconds,and summing the scores provided by individual monitors.

1: bitterness is hardly felt

2: bitterness slightly remains

3: bitterness remains to some extent

4: slightly strong bitterness remains

5: strong bitterness remains

[Evaluation Criteria]

In the case where the average value obtained from the 5 stage evaluationdone by 10 panelists was 1.0 or more and 3.0 or less, it was evaluatedthat bitterness is little and the ester was suitable in uses for keepingit in the mouth (shown as “Good” in Table 1). On the other hand, in thecase where the value is 3.0 or more and 5.0 or less, it was evaluatedthat bitterness was felt and the ester was not suitable in uses forkeeping it in the mouth (shown as “Bad” in Table 1).

TABLE 1 Step a Step b Step c Synthetic Synthetic Water Amount of Amountof Reaction Reaction Reaction product process content after methanolcatalyst temperature pressure time (hour) Note 1 Note 2 dehydrationadded (wt %) Note 3 (Wt %) (° C.) (kPa) Note 4 Example 1 1 A 0.10 3.60.4 170 6.5 8 Example 2 2 A 0.12 2.0 0.5 190 6.5 5 Example 3 3 A 0.253.8 0.2 150 Normal 8 Pressure Example 4 1 A 0.10 3.6 0.4 180 Normal 12Pressure Comparative 1 B 0.15 4.0 0.25 170 6.5 20 Example 1 Comparative1 A 2.50 3.6 0.4 170 6.5 17 Example 2 Comparative 1 A 0.15 0.0 0.4 1706.5 15 Example 3 Comparative 1 A 0.20 4.95 0.05 170 6.5 25 Example 4Comparative 1 A 0.13 2.5 2.5 170 6.5 5 Example 5 Comparative 1 A 0.103.6 0.4 110 6.5 30 Example 6 Comparative 1 A 0.12 3.6 0.4 230 6.5 4Example 7 Comparative 1 A 0.11 3.6 0.4 170 6.5 8 Example 8 Comparative 1B 0.14 — 0.25 230 Normal 5 Example 9 Pressure Comparative 1 B 0.11 —0.25 230 Normal 5 Example 10 Pressure Step d Aldehyde content Just aftersynthesis After 6 months Reaction of Component Bitterness Bitternesstemperature B (ppm) Score Judgment Score Judgment Example 1 100 5.0 13Good 15 Good Example 2 100 7.4 14 Good 14 Good Example 3 100 6.5 20 Good21 Good Example 4 120 5.0 25 Good 26 Good Comparative 100 5.0 35 Bad 38Bad Example 1 Comparative 100 5.0 32 Bad 35 Bad Example 2 Comparative100 5.0 28 Good 34 Bad Example 3 Comparative 100 5.0 38 Bad 42 BadExample 4 Comparative 100 5.0 37 Bad 41 Bad Example 5 Comparative 1005.0 35 Bad 40 Bad Example 6 Comparative 100 5.0 33 Bad 36 Bad Example 7Comparative 150 5.0 35 Bad 39 Bad Example 8 Comparative 100 5.0 22 Good32 Bad Example 9 Comparative 100 5.0 28 Good 36 Bad Example 10 Note 1:1: Polyoxyethylene (20) sorbitan monooleate 2: Polyoxyethylene (20)sorbitan monostearate 3: Polyoxyethylene (20) sorbitan monolaurate Note2: A: Transesterification method (a method of reacting a fatty acidmethyl ester with a sugar) B: Direct acid method (a method of reacting afatty acid with a sugar) Note 3: Sodium carbonate in ComparativeExamples 1, 9, and 10 and sodium methoxide in other examples Note 4:Time until the spot of the fatty acid methyl ester (in the case oftransesterification) or the fatty acid (in the case of direct acidmethod) as a raw material disappears on thin-layer chromatography

In Examples 1 to 4, not only the bitterness just after synthesis butalso the bitterness after the lapse of 6 months are reduced in allcases.

Comparative Examples 1, 2, and 4 to 8 are performed under out of theconditions of the invention and bitterness was felt just after synthesisin all cases.

In Comparative Example 3, methanol is not added at the time when thecatalyst is added. In this case, the bitterness just after synthesis wasreduced but the bitterness after the lapse of 6 months remarkablyincreased.

In Comparative Example 9, as in Patent Document 2, the sorbitan fattyacid ester is produced by the direct acid method, followed by apurification treatment with Kyoward. In this case, bitterness wasreduced just after synthesis by the purification treatment. However,after the lapse of 6 months, it was found that bitterness increased.

In Comparative Example 10, as in Patent Document 1, the sorbitan fattyacid ester is produced by the direct acid method, followed by apurification treatment with steam. In this case, bitterness was reducedjust after synthesis by the purification treatment. However, after thelapse of 6 months, it was found that bitterness increased.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

The present application is based on Japanese Patent Application No.2008-016158 filed on Jan. 28, 2008, and the contents are incorporatedherein by reference. Also, all the references are incorporated as awhole.

1. A process for producing a polyoxyethylene sorbitan fatty acid estercomprising reacting an ester (component A) of a fatty acid having 10 to22 carbon atoms and a monohydric alcohol having 1 to 3 carbon atoms withat least either (component B) of sorbitol and sorbitan to obtain asorbitan fatty acid ester and adding ethylene oxide to the sorbitanfatty acid ester, thereby producing a polyoxyethylene sorbitan fattyacid ester, which comprises: (a) a step of providing the component B inthe form of a 50 to 90% by weight aqueous solution to mixing it with thecomponent A, and performing dehydration until a water content in thesystem reaches 1.0% by weight or less based on a total weight of thecomponents A and B; (b) a step of adding 1 to 10% by weight of amonohydric alcohol having 1 to 3 carbon atoms and 0.1 to 1.0% by weightof an alkali catalyst based on the total weight of the components A andB at 50 to 90° C.; (c) a step of performing a transesterificationreaction under a nitrogen stream at a reaction temperature of 140 to190° C. to obtain a sorbitan fatty acid ester; and (d) a step of addingethylene oxide to the sorbitan fatty acid ester at a reactiontemperature of 70 to 130° C.
 2. The process according to claim 1,wherein the transesterification reaction in the step (c) is performedunder a reduced pressure of 1 to 20 kPa.
 3. The process according toclaim 1 or 2, wherein an aldehyde content of the component B is 50 ppmor less.